Went to the perinatal specialist last week. They don't think it's a cyst now but the can't say for sure. They're calling it a uterine defect. The extra sack is possibly from my previous c section. The way they explained it is that there should be three layers between the baby and this extra sack; the uterus, a thin layer or mucus, then a layer of muscle. The problem is that by the looks of it, the layer of muscle is missing (maybe it didn't heal back together after my c section). So with there only being two thin layers between the sack and the baby, they're scared that it's going to burst and cause problems. I go for another sonogram this Friday. Then next week I'll be 24 weeks so I'll start going twice every week for a sonogram and stress test. Also, next week they're giving me steroid 2 injections, 24 hours apart, to strengthen the baby's organs in case I go early. They're planning on doing a c section when I'm 36 or 37 weeks, if I make it that far. Hoping for the best, preparing for the worst.